Pentofuranosyl nucleosides are nucleosides in which a pentofuranose ring, that is, a heterocyclic five-membered ring, which is derived from pentose sugars, is bonded to the heterocyclic ring of a pyrimidine or purine base. Substituents can be present on each of both rings. Ring atoms as well as pendant hydroxy and amino groups can be replaced by other atoms or groups whereby a large number of possible variations is created.
Different pentofuranosyl nucleosides are known for their anti-viral activities. Nucleosides for example with a 2-deoxy-2-fluor-D-arabinofuranose moiety have a potential anti-viral activity against herpes viruses and are among the most active anti-herpes agents. Compare De Clercq et al., Biochem. Pharmacol. 33, 2159 (1984). A number of these nucleosides has already been tested in vivo. Their antiviral activity is dependent on the presence of a virus-specific thymidine kinase, whereby they are converted into the corresponding 5'-monophosphate derivatives. The monophosphates are further phosphorylated by cellular enzymes to triphosphates which then inhibit the viral DNA polymerase.
In the same manner base modifications of the natural 2'-deoxy nucleosides can provide these nucleotides with an anti-viral activity against herpes viruses. This activity of for instance 5-iodo-2'-deoxyuridine and E-5-(2-bromo vinyl)-2'-deoxyuridine is likewise dependent on a virus-specific thymidine kinase. Compare De Clercq et al., in Developments in Anti-viral Chemotherapy, pages 21-42 (1980), Ed. Collier and Oxford, Acad. Press.